This invention relates to the art of wheel alignment diagnostic systems and, more particularly, to improvements permitting alignment with respect to an equilibrium center line wherein the vehicle's thrust direction coincides with the vehicle's body center line.
The invention is particularly applicable for use in conjunction with aligning all four wheels of a unibody vehicle and is described with particular reference thereto; although, it is to be appreciated that the invention may be used in various vehicles whether frameless or not.
Historically, damaged vehicle bodies are repaired at body shops for correction of the body damage and of any frame damage. Wheel alignment work is done at a separate, and frequently independent, alignment shop. The typical alignment shop is not provided with equipment to diagnose wheel alignment problems that may be caused by body misalignment as opposed to damaged or improperly installed suspension components. Until recently, with the advent of unibody vehicles, this deficiency in the alignment shop has not been a significant problem since a typical vehicle had a solid axle rear drive mounted to a frame and the front wheels were aligned based on the assumption that the frame was not bent and that the solid axle rear drive was in proper alignment relative to the frame.
However, with the advent of today's unibody vehicles, the body is also the structure of the vehicle and the suspension is often fastened directly to the body. There is often little or no suspension adjustment. Thus, there may be no castor and no camber adjustment and only toe adjustment. Consequently, body alignment and suspension alignment are closely related, particularly with respect to unibody vehicles.
An alignment shop can no longer assume that the chassis is straight. In making a wheel alignment analysis there should be a determination as to whether it is a body related problem or is it in the suspension itself. Thus, an alignment shop now needs to be able to measure like a body shop. Alignment equipment should be capable of measuring the suspension relative to the body center line.
The prior art respecting wheel alignment apparatus is replete with examples wherein an active sensor, such as a light beam projector, is mounted directly to a vehicle component, such as a steerable wheel. A light beam is then projected at a target mounted to the nonsteerable wheel. The alignment information relative to the nonsteerable wheel is used in determining what the steerable wheel alignment should be. An example of such prior art is found in the patent to Hunter, U.S. Pat. No. 4,265,537. Such prior art makes an assumption with respect to the correctness of the alignment of the nonsteerable wheel relative to its mounting structure. If the rear axle of the vehicle being analyzed is bent, or the frame to which it mounted is bent, then the reference to such a rear wheel is not an accurate reference point. Additional examples of wheel alignment systems employing active alignment equipment operatively mounted on either the steerable or nonsteerable wheels or both are found in the patents to Hunter, U.S. Pat. No. 4,302,104 and Lill, U.S. Pat. No. 4,402,603.
Even body shop equipment for checking alignment of vehicle frame and body portions typically includes mounting active sensors to the frame or body parts. An example is found in the patent to Eck, U.S. Pat. No. 4,330,945.
The prior art does provide a teaching of employing active elements, such as laser transmitters, which are mounted independently of a vehicle body or suspension system and with the laser transmitters being mounted on a portable support device. This is shown in the patent to Eck, U.S. Pat. No. 4,338,027. However, while this patent provides such externally mounted laser transmitters, there is no recognition in the patent of determining the thrust direction of the vehicle and its relationship to the vehicle's body center line.
The VanBlerk U.S. Pat. No. 4,383,370 is similar to the earlier mentioned patents in that it employs active sensor units mounted to the vehicle's wheels. However, this patent does present a teaching that the thrust line of a wheel system should correspond with the geometric axis of the frame. There is, however, no recognition representative of the desirability of using light transmitting means mounted externally of the vehicle for determining the relationship of the vehicle's thrust line to the vehicle's body center line.
The present invention includes a recognition that present day wheel aligning equipment, with the exception of Eck U.S. Pat. No. 4,338,027, typically mount the active sensing transducer to the vehicle's body. This is a basic assumption respecting the correctness of a vehicle component. The present invention makes no assumption regarding the correctness of any vehicle component, such as the chassis, frame, axle, body, etc. Instead, the active sensing components are located externally and totally independent of the vehicle.
Another recognition made by the present invention is the desirability of relating the vehicle's thrust direction or thrust line to the vehicle's body center line. When these two are coincident, they produce an equilibrium center line at which all force components of the left side of the vehicle are equal to and opposite to all of the force components of the right side of the vehicle. When these force components are in harmony, then the vehicle is in equilibrium, and the correct direction of travel of the vehicle will be along that defined by the equilibrium center line.
In practicing the invention, it is contemplated that the relationship of the vehicle's thrust line to the body center line will be determined. If the two coincide, then the vehicle is in harmony and an equilibrium center line is defined with all force components being in balance. With this accomplished, the wheels may then be aligned with respect to the equilibrium center line. If the vehicle's thrust line and body center line are not coincident, then a decision should be made as to whether it is economically practical to bring the two into harmony. This should be practical in vehicles having adjustable rear ends. Thus, most independent rear axle vehicles may be adjusted as described in their vehicle service manuals in order to bring the vehicle thrust line into coincidence with the body center line, producing an equilibrium line. In solid rear axle vehicles it may be necessary to make alterations to readjust the axle carrier mechanism to bring the vehicle into equilibrium. In such a solid rear axle vehicle, an insurance company, in a wrecked vehicle situation, may choose to scrap the vehicle rather than incur the expense of repositioning the axle carrier. If there is a minor variance between the thrust line and the body center line, and, providing no driveability problem exists, a compromise may be made by aligning the vehicle's suspension to the thrust line, thereby avoiding the cost of repositioning the axle carrier.